U.S. Pat. No. 3,591,131 discloses a tank car bottom outlet valve comprising a ball valve operable from the bottom in which the discharge spout is laterally spaced from the depending ball valve operator. The housing for the ball valve is shaped such that lading can only enter the housing during unloading in one direction. In leaving the tank the lading must make a 90.degree. turn. This results in slow unloading rates and cavitation of the housing. The unloading spout and depending operator are shearable in the event of impact to maintain the ball valve in seated position within the tank.
In U.S. Pat. No. 3,661,355 the discharge spout is aligned with the ball valve. However, the lading must move vertically up within the housing to enter the discharge valve. Thus all of the lading cannot be removed from the tank during unloading. The embodiment shown in FIG. 3 of this patent is similar to U.S. Pat. No. 3,591,131.
In U.S. Pat. Nos. 3,588,042 and 4,162,690 a ball valve is shown located in a horizontal transfer pipe which is operable from above the ball valve.